Solventborne coating compositions typically include a primary binder resin, a crosslinker, a pigment or pigments to improve the aesthetics of the coating composition, and other coating additives such as solvents, flow and appearance control agents, fillers such as extender pigment, and the like.
It is understood in the art that the pigment is incorporated into the solventborne coating compositions via a pigment dispersion. The pigment dispersion is derived from dispersion of the pigment into a grind resin. More specifically, a mill, such as a ball mill, grind mill, or continuous mill, is utilized to incorporate the pigment into the grind resin. The mill integrates the pigment into the grind resin until a desired particle size of the pigment is achieved, and until the pigment is appropriately wetted by the grind resin and uniformly dispersed throughout the grind resin.
The grind resins of the prior art including, but not limited to, polyacrylic-based resins, have proven to be inadequate for use as a grind resin for dispersing pigment usable in solventborne coating compositions. The grind resins of the prior art are ineffective because these resins are unable to withstand mechanical forces exerted by the mill when integrating the pigment. These grind resins are also deficient in wetting the pigment and in maintaining the pigment dispersed throughout the grind resin. Instead, with the grind resins of the prior art, such as the polyacrylic-based resins, the pigment tends to coagulate or settle resulting in poor stability and inadequate ‘shelf life’ of the pigment dispersion.
Furthermore, it is known in the art that the insufficient resistance to mechanical forces, the insufficient wetting, and the coagulation and/or settling as described above lead to poor color travel in solventborne coating compositions. The poor color travel associated with solventborne coating compositions contributes to color matching problems between solventborne and waterborne coating compositions. For example, with a phthalocyanine-based blue pigment, a waterborne coating composition is redder at the ‘flop’ viewing angle and greener at the ‘face’ viewing angle relative to the color of the same phthalocyanine-based blue pigment in a solventborne coating composition. In other words, the waterborne coating composition with such a pigment has much larger color travel relative to the solventborne coating composition with the same pigment. This difference in the amount of color travel between waterborne and solventborne coating compositions is particularly troublesome for vehicle assembly plants that utilize waterborne coating compositions as primary body paints and solventborne coating compositions as repair and/or bumper paints. Consequently, excessive ‘tinting’ or color modification takes place with both waterborne and solventborne coating compositions.
These prior art grind resins also tend to have increased viscosities and, as understood in the art, increased viscosities typically inhibit the amount of pigment that can be incorporated into the grind resin. As a result, pigment dispersions that utilize the grind resins of the prior art cannot attain sufficient pigment-to-binder ratios while maintaining acceptable gloss and appearance in a film of the coating compositions. Also, due to the increased viscosity, these grind resins often require additional solvent and other additives which increases the overall volatile content of the pigment dispersion—a characteristic that is undesirable throughout the coating industry.
In sum, the prior art grind resins, as detailed above, are characterized by one or more inadequacy. Due to the inadequacies identified in the prior art, it is desirable to provide a novel polymeric pigment dispersant to be utilized as a grind resin for pigments and a method of preparing the polymeric pigment dispersant. It is advantageous that the polymeric pigment dispersant according to the subject invention effectively wets pigment, uniformly disperses pigment, and provides increased pigment-to-binder ratios accompanied with acceptable color, gloss, and appearance in the film of the coating composition.